Process for the oxidation of ticl4 to produce tio2



United States Patent 3,352,639 PROCESS FOR THE OXIDATION OF TiCl T0PRODUCE TiO John Peter Wikswo, Ridge Drive, Va., assignor to AmericanCyanamid Company, Stamford, Conn., a corporation of Maine No Drawing.Filed Feb. 17, 1965, Ser. No. 433,491 10 Claims. (Cl. 23-202) ABSTRACTOF THE DISCLOSURE The present invention relates to an improved method ofpreparing TiO by the reaction of titanium tetrachloride and relativelypure carbon monoxide with oxygen in the presence of a small amount ofhydrogen sulfide. This invention is based upon the discovery thathydrogen sulfide in relatively small amounts, not only exerts acatalytic effect upon the reaction, but also produces an additionalbeneficial effect beyond that produced by water alone and that it doesthis without the undesirable hydrolysis of the feed materials occurringwhen water alone is used.

This invention relates to an improved method of burning TiCl, to produceTiO pigment.

In the manufacture of TiO pigment by the combus tion of TiCl it is knownthat a small amount of water will serve to nucleate the formation of TiOpigment particles. As to such systems, it was found by previous workersthat at least .05% by volume of water, based on the total combustionmixture, shall be used in order to obtain a beneficial nucleatingeffect. However, these findings have been discovered in connection withwhat is com monly referred to as a turbulent-type burner. Contrary towhat might be expected, it was found that a beneficial effect couldresult from using water in amounts less than 0.05% in a combustionsystem involving a laminar flame burner of the type described in U.S.Patent No. 3,121,641. One significant difference between the two systemsis that in the laminar flame burner, CO is one of the ingredients of thecombustion feed mixture which serves to furnish additional heat to thatgenerated by the combustion of TiCl to TiO Further, in a laminar flameburner, the relatively smaller beneficial amounts of water, viz., from.005% to .06% by volume, based on the total feed mixture, appear tocatalyze the combustion of CO to CO and the heat thus evolved appears tohave a beneficial effect on pigment formation. From theseconsiderations, it is apparent that the nature of the reactionsoccurring in a turbulent-type burner is different from that taking placein a laminar-flow burner.

In a laminar-flame burner, it is customary to use screens in the feedinlets to create a laminar-flow condition. The presence of water in thefeed may tend to hydrolyze the TiCl to produce a hydrolytic product thatmay tend to deposit on the screens of the feed tubes. The deposition ofthe hydrolytic product tends to interfere with the flow of the feedmaterial, thus leading towards an undesirable condition. To avoid thistendency, additional materials were examined from the standpoint ofdetermining how the combustion reaction could be benefited without thepossibility of depositing hydrolytic product in the feed inlet. Quiteunexpectedly, we have discovered that hydrogen sulfide in relativelysmall amounts not only exerts a catalytic efiect but also produces .anadditional beneficial effect on the combustion reaction beyond thatproduced by water only and that it does this without the undesirablehydrolysis of the feed materials occurring in the burner inlet. Also,quite surprisingly, it was found from a series of experiments which ledto the present discovery that propane and HCl gave no beneficial effectin the laminar flame system, which illustrates that the benefitresulting from the use of H 3 involves a phenomenon other than merelyforming H O in situ during the combustion reaction.

Accordingly, an object of this invention is to provide an improvedmethod for the production of TiO pigment.

Another object of this invention is to provide a method of producingpigmentary TiO of an exceptionally high tint tone and tinting strength.

Other objects and advantages of this invention will become apparent fromthe following description and explanation thereof.

By means of the present invention, the feed mixture of TiCl oxygen,aluminum chloride, H 5 and CO is fed to a laminar-flow burner underconditions suitable for the production of pigmentary TiO The combustionreaction is conducted at a temperature of about 1400" to 1850 C., andmore usually about 1450 to 1600 C. The amount of CO present in the feedmixture is measured as a volumetric ratio of CO to TiC1 and in general,this ratio is about 0.1 to 3.0: 1, more usually about 0.3 to 1.0:1. Thetotal feed mixture being fed to the combustion zone is determined as avolumetric space velocity, i.e., the cubic feet per minute of feedmixture, measured at 25 C. at 1 atmosphere of pressure, per square footof flow area in the feed mixture inlets leading to the burning zone.Generally, the volumetric space velocity is about 15 to 45, and moreusually about 20 to 40. The combustion reaction takes placesatisfactorily under essentially atmospheric pressure, however, a higheror lower pressure may be employed. The oxygencontaining gas, measured asthe excess over the stoichiometric amount needed to react with all theTiCl (and assuming that a stoichiometric amount of oxygen is present toact with all the CO), is about 5 to excess, on a volumetric basis, andmore usually about 40 to 80% on the same basis. Aluminum chloride mayalso be present in the feed mixture in an amount of about 1 to 5% byweight, more usually about 2 to 3% by weight, measured as A1 0 in theTiO finished product. The amount of H 8 present in the feed mixture mayvary from about ,002 to .06% by volume, based on the total feed, andmore usually .01 to .04% by volume on the same basis. Water may also bepresent in the feed mixture in an amount ranging from about .005 to .06%by volume, based on the total feed mixture, and more usually to .02 to.04% by volume on the same basis. The conditions described above for thereaction involving production of pi-gmentary TiO may be varied outsidethe ranges specified above without departing from the spirit of theinvention.

In a laminar-flame burner of the type described in U.S. Patent No.3,121,641, the feed material is divided into two main streams which areintroduced into the burning zone from diametrically opposed directions.The combustion flames resulting from the burning of each stream opposeeach other to form two adjacent continuous flame fronts which contacteach other without significant intermixing between the materials of theundivided flames. The introduction of the feed mixture into thecombustion zone may be accomplished in a variety of ways, however, in acommercial operation, it is preferred that dampening screens be presentin the feed tubes of the burner system. The dampening screens reduce anytendency towards flow turbulence which may tend to occur from thepassage of the gas within the confined area of the feed conduits. Thefeed mixture may be preheated to a temperature of about to 300 C., moreusually about 200 to 250 C. The oxygen-containing gas which is used inthe combustion reaction may be either pure oxygen, .air or enriched air.For reasons of efiiciency of operation it is preferred thatpure oxygenbe used as the source of oxygen for the reaction.

We have also discovered that large excesses of oxygen have a beneficialeffect on the quality of the pigmentary TiO The greatest benefit isobtained when using from about 80120% excess oxygen. The excess oxygenappears to behave as a promoter of the Ti product, and coning brick,which replaced the cooling jacket shown in the patent. The experimentswere made using the reaction conditions shown in Table I below,including a reaction pressure of essentially one atmosphere. Theapparatus and method of operation described in the patent are herebyincorporated by reference and made a part of the present specification.

TABLE I Run No 1 2 3 4 5 i 6 l 7 8 9 TiCh, lb. mol/hr 3.2 3.2 3.2 3-23-2 3.2 3.2 3.2 3,2 Oxygen, molar excess. 80 S0 80 80 8O 80 80 8O 80CO/TiCh, molar excess. .55 .55 .55 55 .55 .55 55 .55 ,55 Vol. spacevelocity 31 3 31 3 d1 31 31 31 31 E20, Vol. percent (total feed) 0 O 0 00 .0185 0185 0063 .0063 HgS, Vol. percent (total feed) 0 0061 .0122 0184.0243 .0063 0 0 .0061 Combustion Ternp., C t 1, 505 1. 505 1, 505 1, 5051,505 1, 505 1,505 1, 505 1, 505 Pigment quality, Tint Tone V Br Br 2B1'1 3 Br 1 Br .3 B1 1. 5 Br 2. 6 Br-7 B1-7 Tinting Strength 1, 200 1,650 1, 6 0 705 670 1, 675 1, 650 1, 470 1, 630 Pi ment ualit round): 3

g Tint %0ne, V Bl Bll 1310.5 B11 B11 1311 B1 2.2 Brfi B1 1 TintingStrength 1, 310 7 0 7 775 7 0 l, 740 1, 740 1, 575 1, 770

1 TiCll contains 3 mol percent A101 sequently it is possible to reducethe amount of aluminum chloride and/or water for the reaction by the useof such large excesses of oxygen. Without being bound by any theory, itappears that the large excess of oxygen creates a beneficial mass-actioneffect which makes possible reducing the amount of H 0 and H 5 which maybe needed to obtain beneficial effects.

The H S may be added by a variety of methods to the total feed mixture.It can be added directly to the CO stream, which is later combined withthe other ingredients of the feed mixture. Alternatively, it may headded to the vaporous mixture of aluminum chloride and TiCl Generally,however, the H 8 is added to the CO stream in an amount of about 200 to4000 ppm, and more usually about 600 to 1800 ppm. In any case, theamount of H 8 in the CO stream will be sufficient to provide the desiredfinal concentration of H 8 in the total feed material.

When water is added to the reaction, it may be injected directly intothe feed mixture or along with any one or more of the ingredientsthereof. In commercial practice it is preferred that the CO stream behumidified in order to have an intimate association of the twomaterials. This can be accomplishedby drying a wet stream of CO to thedesired water concentration, or in the case of dry CO, the water can beadded by passing the CO through a water tower. By whatever method isemployed, generally the water content of the CO stream may be from about400 to 4000 p.p.m., and more usually about 1200 to 1800 ppm. In anycase, the amount of water present in the CO stream will provide thedesired final water concentration in the total feed stream.

Aluminum chloride may also be added to the feed mixture containing TiC1The aluminum chloride promotes theformation of rutile pigmentary TiO andtherefore is desirable for commercial practice. The aluminum chloride isfirst combined with TiCl This may be done by vaporizing a mixture orsolution of aluminum chloride and TiCL, by heating the same to atemperature of about 140 C. to 250 C., more usually about 175 to 200 C.,at a pressure of about 1 to 120 p.s.i.g., more usually about to 45p.s.i.g. The vaporous mixture of TiCl and AlCl may be readily combinedwith the other ingredients of the total feed mixture, such as CO and H Sprior to entering the burner To provide a better understanding of thepresent in vention, experiments were made in a burner of the typedescribed in U.S. Patent No. 3,121,641, except that the burner tubesemployed in the experiments reported below were 15 inches in diameterand the feed gases were introduced into the burner tubes without thetangential swirl. The hood of the burner was aluminum lined withinsulat- What is claimed is:

1. A process for producing titanium dioxide which comprises reactingtitanium tetrachloride with an oxygen containing gas in the presence ofa gaseous mixture consisting essentially of carbon monoxide and hydrogensulfide, the hydrogen sulfide being present in an amount of about .002to .06% by volume of the total gas, the volumetric ratio of carbonmonoxide to titanium tetrachloride being about 0.1 to 3.0: l, at atemperature of about 1400 C. to 1850 C., the oxygen being employed in astoichiometric excess of about 5 to 120% by volume, and a volumetricspace velocity of the total gas being about 15 to 45.

2. A process for producing titanium dioxide which comprises reactingtitanium tetrachloride with oxygen in the presence of a gaseous mixtureconsisting essentially of carbon monoxide and hydrogen sulfide, thehydrogen sulfide being present in an amount of about .01 to .04% byvolume of the total gas, the volumetric ratio of carbon monoxide totitanium tetrachloride being about .3 to 1.0:1, ata temperature of about1450 to 1600 C., the oxygen being. employed at a stoichiometric excessof 40 to by volume, and a volumetric space velocity of the total gasbeing about 20 to 40.

3. The process of claim 1 being further characterized by the additionalpresence of water in an amount of about .005 to .06% by volume of thetotal gas.

4. The process of claim 2 being further characterized by the additionalpresence of Water in an amount of about .01 to .04% by volume of thetotal gas.

5. The process of claim 1 wherein the oxygen containing gas is oxygen.

6. The process of claim 2 being further characterized by the additionalpresence of about 1 to 5% aluminum chloride measured as A1 0 in thefinal pigment.

7. In a process of producing titanium dioxide by reacting titaniumtetrachloride with an oxygen containing gas by means of diametricallyopposed reactant streams to form two parallel laminar flames, theimprovement which comprises reacting said materials in the presence of agaseous mixtnreconsisting essentially of carbon monoxide and hydrogensulfide, the hydrogen sulfide being present in an amount of about .002to .06% by volume of the total gas, the volumetric ratio of carbonmonoxide to titanium tetrachloride being about .01 to 3.0:1, at atemperature of about 1400 to 1850 C., the oxygen being employed in astoichiometric excess of about 5 to by volume and a volumetric spacevelocity of the total gas being about 15 to 45.

8. In a process of producing titanium dioxide by reacting titaniumtetrachloride with oxygen by means of diametrically opposed reactantstreams to form two parallel laminar flames, the improvement whichcomprises reacting said materials in the presence of a gaseous mixtureconsisting essentially of carbon monoxide and a small amount of hydrogensulfide, the hydrogen sulfide being present in an amount of about .01 to.04% by volume of the total gas, the volumetric ratio of carbon monoxideto titanium tetrachloride being about 0.3 to 1.021, at a temperature ofabout 1450 to 1600 C., the oxygen being employed in a stoichiometricexcess of about 40 to 80% by volume, and a volumetric space velocity ofthe total gas being about 20 to 40.

9. The process of claim 8 being further characterized by the additionalpresence of about .01 to .04% by volume of water.

10. The process of claim 8 being further characterized by the additionalpresence of Water in an amount of .01 to .04% by volume of the total gasand about 1 to 5% by Weight aluminum chloride measured as A1 0 in thefinished pigment.

References Cited UNITED STATES PATENTS 911,494 2/1909 Hall 233.11,678,630 7/1928 Bahr 23--3.1 1,807,528 5/1931 Hiatt 233.1 2,635,946 4/1953 Weber et al. 23202 2,689,781 9/1954 Schaumann 23202 2,823,9822/1958 Saladin et al. 23-202 2,957,753 10/1960 Nelson et a1 232023,069,282 12/1962 Allen 23202 3,121,641 2/1964 Wiksmo et al. 232023,224,836 12/1965 Allen et al. 23202 OSCAR R. VERTIZ, Primary Examiner.

EDWARD STERN, Assistant Examiner.

1. A PROCESS FOR PRODUCING TITANIUM DIOXIDE WHICH COMPRISES REACTINGTITANIUM TETRACHLORIDE WITH AN OXYGEN CONTAINING GAS IN THE PRESENCE OFA GASEOUS MIXTURE CONSISTING ESSENTIALLY OF CARBON MONOXIDE AND HYDROGENSULFIDE, THE HYDROGEN SULFIDE BEING PRESENT IN AN AMOUNT OF ABOUT .002TO .06% BY VOLUME OF THE TOTAL GAS, THE VOLUMETRIC RATIO OF CARBONMONOXIDE TO TITRANIUM TETRACHLORIDE BEING ABOUT 0.1 TO 3.0:1, AT ATEMPERATURE OF ABOUT 1400*C. TO 1850*C., THE OXYGEN BEING EMPLOYED IN ASTOICHIOMETRIC EXCESS OF ABOUT 5 TO 120% BY VOLUME, AND A VOLUMETRICSPACE VELOCITY OF THE TOTAL GAS BEING ABOUT 15 TO 45.